1. Field of the Invention
The present invention relates to a control system for communications between driving units and control units.
2. Related Background Art
Data for driving each component of an image forming apparatus or detected data representative of the status of each component is stored in a register located at a partial area of an address space of a CPU which controls the whole of the apparatus. The contents of this register are directly supplied to a transistor which drives a load such as a clutch of the apparatus or to a sensor which detects a presence/absence of a recording sheet.
Specifically, CPU which controls the whole of the apparatus reads data in an input register (one type of the above-described register dedicated to data input) to thereby monitor a status detected with a status detecting unit, or writes data in an output register (one type of the above-described register dedicated to data output) to thereby drive each component of the apparatus.
With the above-described conventional structure of the apparatus, however, it is necessary to mount input registers, output registers, and driver registers near CPU which controls the whole of the apparatus. This is one factor of making the size of a control circuit board large.
Control signal lines are led out of and pulled into the control circuit board, as many as the number proportional to that of those sensors which detect a presence/absence of a clutch for driving a load, a recording sheet or the like. A number of control signal lines are therefore disposed at the periphery of the control circuit board, so that difficulties of effective usage of mounting space and of assembly are becoming conspicuous. Such difficulties become serious as the length of each control signal line from the control circuit board to the load or sensor becomes long, and the number of such control signal lines becomes large as the apparatus becomes large and sophisticated.
The control circuit board is designed to be optimum in accordance with the number of sensors and loads such as a clutch used by the apparatus. Therefore, it is required to redesign the control circuit board each time the configuration of the apparatus is changed.
In order to solve the above problems, one method has been proposed in which processes heretofore performed by one control CPU are distributed to a plurality of control CPUs to physically divide one control circuit board. With t his method, however, other problems occurs such as overhead of communication protocols and high cost of additional CPUs, ROMs and RAMs caused by the division of CPU. Furthermore, use of this method makes it difficult to realize a control circuit board having high operability between different applications.